The Windows Incident Response Blog is dedicated to the myriad information surrounding and inherent to the topics of IR and digital analysis of Windows systems. This blog provides information in support of my books; "Windows Forensic Analysis" (1st thru 4th editions), "Windows Registry Forensics",
as well as the book I co-authored with Cory Altheide, "Digital Forensics with Open Source Tools".

Tuesday, October 21, 2014

Windows Event Logs

I have no idea what that means. I'm going to assume that what Dan's looking for is information regarding Event Logs records that have been found useful or valuable to forensic analysts, or potentially could be.

EVT vs EVTX
Windows XP is no longer supported by Microsoft, but there are still XP and 2003 systems out there, and as such, some of us are still going to need to know the difference between Event Logs (XP, 2003), and Windows Event Logs (Vista+).

Besides the binary differences in the records and Event Log files themselves, on XP/2003, there were three main Event Log files; System, Application, and Security. On my Windows 7 system, a 'dir' of the winevt\Logs folder reports 143 files. So, there is a LOT of information being recorded by default on a Windows 7 system; while not all of it may be useful to you, there is a great deal of information that can be extracted from the logs when used properly.

Wevtx.bat
When I released Windows Forensic Toolkit 4/e, one of the things included in the additional materials is a batch file, wevtx.bat. What the batch file does is use LogParser to parse a directory full of .evtx files, and then parse those entries into TLN format for inclusion in a timeline. The tool evtxparse.exe, used by the batch file, makes use of a mapping file (i.e., eventmap.txt) to map event source/ID pairs to an artifact category tag. As such, when the entry in written to a timeline, records such as "Microsoft-Windows-Security-Auditing/4624" are prepended with an appropriate tag (i.e., "[Logon]"), based on the artifact category.

I really love this tool! What I like about it is that it's easy to update (eventmap.txt is just a text file), I can add comments to it to show the source of the information I used to map an event record to something specific, and it acts as a fantastic little repository for all of my past experiences. Not only is it a great repository, but it's incorporated right into the tools that I use on just about every engagement.

Records
Here are some of the event source/ID pairs that I've found to be useful during investigations, for such things as malware detection, determining the window of compromise, etc. I'll say up front that these records are not 100% infallible, and may not have extremely high fidelity (some do, others don't...), but they've worked quite well for me at one time or another, so I'll share them here.

Microsoft-Windows-DNS-Client/1014 – DNS name resolution timeout; I've used this one more than once to help demonstrate that malware was on a system, even in the face of anti-forensics techniques (time stomping the malware files, deleting the malware files, etc.). It's not a 100%, infallible indicator, but it's worked for me more than once. What has also helped is when this event record was seen; in a timeline, I could see that it occurred shortly after a user logged into a laptop, and before the user connected the system to a WAP. This helped me narrow down the persistence mechanism for the malware.

McLogEvent/257 – McAfee malware detection - McAfee AV may detect malware behaviors (i.e., run from a Temp folder, etc.) without actually detecting the EXE itself. This can be very valuable in helping you determine how malware got onto a system. Also, the AV product may be configured to warn only, and take no action..so, correlate the event records (UTC) to the entries in the McAfee logs (local system time)

Beyond individual event records (source/ID pairs), one of the aspects of the newer versions of Windows (in particular, Windows 7) is that there are a lot of events that are being recorded by default, across multiple Event Log files. What I mean is that when some events occur, multiple event records are recorded, often across different Event Log files. For example, when a user logs into a system at the console, there will be an event recorded in the Security Event Log, a couple in the Microsoft-Windows-TerminalServices-LocalSessionManager/Operational.evtx log, and a couple of events will also be recorded in the Microsoft-Windows-TaskScheduler/Operational.evtx log. Alone, each of these individual events may get little attention from an analyst, but when placed together in a timeline, they leave an indelible mark indicating that a user logged into the system.

Now, what's really great about this is that some of the Event Logs "roll over" faster than others. As such, some of the source/ID pairs that are part of an indicator cluster may have been expired from their respective Event Logs. However, the remaining source/ID pairs in the cluster will still provide a very good indicator that that event in question took place. This is particular useful for infrequent events, and I've used this information more than once to demonstrate repeated activity going back weeks and even months prior to what was thought to be the date of interest.

Anti-Forensics
Event auditing is one of those things that just happens in the background on Windows systems. This is great, because sometimes Event Log records can help us determine if anti-forensics techniques have been employed. For example, using Event Log records, you can determine if someone has changed the system time.

During an exam, I found that a system had been infected with malware that installed as a Windows service, and during the installation process, the .exe file had been time-stomped. Fortunately, when the malicious service was installed, an event source/ID pair of "Service Control Manager/7045" was created, indicating that a new service had been installed on the system. I was able to correlate that information with other sources (MFT, etc.) to better determine the correct time of when the malicious .exe was created on the system, and nail down the infection vector.

Carving
If you need to carve Windows Event Log records, for any reason...from unallocated space, memory, the pagefile, whatever...the tool to use is Willi Ballentin's EVTXtract. The "tool" is really a set of Python scripts that you run consecutively against the data in order to recover Windows Event Log records. I've used these scripts a couple of times, and even had a fellow team member use them on an engagement and quite literally recover the "smoking gun".

When carving for deleted records on a Windows XP or 2003 system, I use a custom Perl script that I wrote that's based on some of the code I've released with my books.

Timelines
When all this is said and done, a blog post on just individual Windows Event Log records isn't really all that valuable. Yes, I've created timelines from just a handful of *.evtx files, for use in triage, etc. This has proved to be extremely valuable to me.

4 comments:

This is a fantastic post that is right in line with what I was hoping to receive from the very short (and truly vague) question I put out on Twitter.

I appreciate you taking the time out to write it.

It's one thing to list a bunch of Event IDs and explain what they are. It is a completely different (and more valuable) thing to zone in on the forensic aspect of said events based on past experience. To identify and document what's worked for you in the past not only helps me as an investigator, but it helps anyone who is curious and willing to understand what they are seeing and potentially what they should be looking for in an investigation. Using the items you've described -- along with the countless other artifacts left on a given system -- one can better grasp what is ACTUALLY happening.

And you hit the nail on the head in the last paragraph -- it's not valuable to just "have a list" of event IDs. The information becomes valuable when you understand and correlate these items with other artifacts and events to more accurately complete the puzzle.

really interesting post. I'm currently working on a system for Windows logs centralisation (and graphing, analysis, search...) based on several open source software.What I miss actually is a way to translate events ID in a human-readable format.Is the 'eventmap.txt' file available somewhere, in a free license for reuse?